1. Field of the Invention
The invention generally relates to fuel cells and more particularly to Solid Oxide Fuel Cell assemblies.
2. Background Information
Most planar solid oxide fuel cells utilize modular cassette type systems. An example of such a system is found in U.S. Pat. No. 7,306,872. In this configuration sheet metal assemblies having a metal interconnect plate and a metal cell-mounting plate are configured so that when they are joined at their perimeter edges to form the cassette, a cavity between the plates results which can contain a gas stream that feeds a fuel cell subassembly attached within the cassette to the mounting plate. Outside of the fuel cell subassembly, the interconnect plate and cell-mounting plate are perforated by openings to form chimney-type manifolds for feeding fuel gas to the anode and air to the cathode, and for exhausting the corresponding gases from the stack. The fuel cell subassembly is attached to, and insulated from, the mounting plate by an insulating glass seal. The mounting plate includes an opening through which one of the electrodes is accessible, preferably the cathode, and through which a conductive interconnect element extends to make contact with the outer surface of the next-adjacent cassette in a stack. The anode openings in the mounting plate and interconnect plate are separated by spacer rings such that the cassette is incompressible. The rings include openings which allow fuel gas to flow from the anode supply chimney into the anode gas channel in the cassette.
In assembling a fuel cell stack from a plurality of cassettes, the mounting plate of one cassette is attached to, and insulated from, the interconnect plate of the next-adjacent cassette by a peripheral insulating glass seal surrounding the interconnect extending from the mounting plate central opening. Thus, each cassette is at the voltage potential of the adjacent cell in a first direction by virtue of contact with its interconnect, and is insulated from the adjacent cell in the opposite direction by virtue of the peripheral insulating glass seal. Thus, the cassettes are connected in electrical series and the supply and exhaust manifolds are formed inherently by the stack-assembly process.
While this process allows the individual cassettes to be individually tested and exchanged when found to be inoperable. This method and configuration has various problems. First, in order for the device to function, the cassettes must be tested, arranged and sealed together. However failure of the glass seals during thermal cycling is a problem. These glass seals tend to have low bonding strength and are typically located on the perimeter of the cassettes and around the gas porting portions. These areas are also where the maximum stresses typically occur during thermal cycling. In these locations, glass cannot be replaced with a conductive material since its insulative properties are required to prevent the cassettes from shorting. What is needed therefore is a device, system, or configuration that provides for increased strength and durability while maintaining appropriate electrical contact. The present invention provides these advantages.
Additional advantages and novel features of the present invention will be set forth as follows and will be readily apparent from the descriptions and demonstrations set forth herein. Accordingly, the following descriptions of the present invention should be seen as illustrative of the invention and not as limiting in any way.